View Full Version : Flat grinder easy solution please

10-13-2014, 10:21 AM
I have a silly hobby of flying model jet planes and part of it involve grinding small ( 7 mm appx flats accurately on 6 mm and 8 mm diameter hardened steel pins. This is to fix Undercarriage parts to their mechaincal devices which raise and lower them.

However the flats need to be flat and appx 1-1.5 max depth but placed where the grub screws that hold them in place can connect squarely with them. So for example an 8mm rod might need two flats 7 mm long and 1 mm deep placed 10mm and 20mm from one end but INLINE with each other. Then at the other end four flats of the same size but 8 mm from the end at 90 deg to each other and one of which is INLINE with the first set at at the other end. Now this may be really easy with a dividing head and a full machine shop but for the modellers workshop its another matter. I have a lathe, a small mill and freestanding drills which spin cutting stones or cutoff discs made by the Dremel company. Anyone with a simple solution would be welcome to advise please.
At present I lay the bar in a vee block and drag it under a fixed spinning cutting disc but sometimes its not spot on INLINE whichever way needed. Idealy using the control of a lathe tool bed or mill bed is ideal but I cannot come up with the solution as yet.
I have some photos of my set up but it seems that the forum does not accept photos, is that correct?



10-13-2014, 12:24 PM

This forum does not accept photos directly, most will use a service like Photobucket etc. or some host themselves (bandwidth thing at some point if popular)

You need to set up some way to index and hold at the same time like this http://www.arceurotrade.co.uk/Catalogue/Collets/5C-Fixtures. That is just an example, really IMO any way you can accomplish both tasks holding and indexing will work.
For example on lathes you can use an extra gear with a pointer (more of a finger) that can act as a stop between the teeth of the gear, then it becomes a matter of having a gear capable of the number of "sides" you need. If what you do is say a flat with another flat 90* from it, if you were using a 36 tooth gear you would count off 9 of those teeth (one quarter of a circle 90*, one quarter of 36 being 9).
If you have to remove the part from how it is held, too long say, you will need a way to make sure that the second flat is oriented as you need to the first and for that you will need access to the first flat while indicating for the second (the indicating action will orient the other flat to the new flat where you want it) so, if the part is inside a lathe spindle for example, it makes it very difficult (that first flat can not be located because it is hidden).

All of the above does work but the simplest way is going to be to mark along the whole length first (round stock in an angle iron say but not fully accurate so what your needs are for accuracy comes into play) and then rotate to orient for the next or other flats and mark those as well.
If the 90* is all you will ever need, once the first flat is milled/ground just using a good 90* angle off the mill table will get you the others by working off that first flat (if you did all at a single end, you would end up with a round shaft that had four flat sides, and, depending on how you did it, you could certainly end up with a nice pretty accurate square).
There are many ways to approach this task, easy, quick, cheap and accuracy will play a part.

10-13-2014, 01:38 PM
Cut two rectangular pieces of wood, mdf, aluminum, etc. Drill and ream a hole through each making sure location is the same for each. Glue steel pins in the holes. You now have an indexer for 90 degrees.